Decending and Landing Mooney techniques

[Skybrd]

I just read an article that informs how to decend and land Mooneys. It's at http://www.mooneyland.com/Properly%20Landing%20a%20Mooney.htm  One of the items that I'm not sure about, concerns decending and keeping from shock cooling the engine. The article says that beside reducing throttle (manifold reduction) to also reduce RPM's by cranking in more prop pitch. They say to pull throttle back to 17 inches then reduce RPM's to 1900 RPM's and that will keep the engine from shock cooling.  Is this a good idea? Additional information from this article seems to be good information. What do you think of this web site's information?  

[Cruiser]

Usually I try to stretch the descent as long as I can to take advantage of the gravity aided speed so I target 350fpm. My experience shows that just reducing MP will keep me at the edge of the yellow. I aim for my leveling off altitude a little earlier than needed so when I level off and hold that altitude the speed will bleed off pretty quickly. Once I slow to gear extention speed I drop the gear and that part of the approach is done. Set up for the pattern and a final check of the gear on short final.

[David Mazer]

I'm pretty sure each Mooney is a little different.  The minimum recommended MP for the Rocket is 25" during descent and 20" is usually the setting for level flight in an approach.  There is no discussion of RPMs but I have been flying at 2200 RPM and leave it there.  What I also do is lean carefully while I decrease MP slowly to maintain TIT.

I have to assume that a normally aspirated J has completely different procedures and I have recently read that there is a lot of question if shock cooling is really the engine killer it was once thought to be.  The prototypical shock cooling model is parachute jumper's planes.  They apparently climb hard to altitude, jumpers away. chop the power, and dive to landing with little impact on their engines life expectancy.  Anyway, what do I know?

[Shadrach]

What you really need to ask your self is "is my engine hot?".... In cruise my CHTs range from ~290 to 335df...so I am of the opinion that my engine is not really hot enough for me to worry much about. I think that "shock cooling" is the stuff of legend, and little else in my opinion. YMMV.

[Lood]

In my F, I normally plan to descend at 300 - 500ft/min and to be at circuit altitude about 2nm before reaching said circuit. This gives me enough time to level out and get the speed under control. All dependant of where I'm flying to of course.
I leave everything as it is and only check the MP about every 1k ft or so to keep it at the original cruise setting, which is normally around 21". This returns good speed but also keeps the IAS in the green. In a situation where an early descend is not possible, I slow down to a much more conservative power setting before starting the descent. Apart from two or three times when I started flying the Mooney, I've never had a problem.

[David Mazer]

Most of my flying is IFR and ATC really doesn't let me descend at 300 - 500 ft/min.  I usually figure a 700 ft/min and dance around power settings and, when required by airspeed or turbulance, speedbrakes to stay in the bottom of the yellow arc or less.  Typical IAS is 175 - 180 unless I am penetrating cumulous or there is turbulance.  Then I shoot for about 155 IAS and use the speedbrakes as required because I won't reduce the power more than about 1" MP/min unless it is an emergency.  Engines are very expensive and I really try not to buy them any more often than I really must!  If shcok cooling is a real problem, I'm avoiding it.  If it isn't, I guess then it isn't a something I will ever care about.

[danb35]

Certainly you can operate your engine however you want, and there's virtually no danger of damaging it by limiting MP reductions to 1"/min, but what's the benefit of doing that?  Presuming you have an engine monitor (and if you don't, you should get one, especially for a Rocket), have you ever checked to see what sort of CHT cooling rate you get?

Lycoming recommends cooling at no more than 50 deg F/min.  Just to be on the safe side, I've set the warning on my engine monitor at 30 deg F/min--and I find it's just about impossible to hit even the 30 deg. limit, much less the 50 deg.  Of course, I have a completely different engine, so your results may well differ, but I suspect you're limiting yourself much more than you need to, even assuming that shock cooling is a legitimate issue.

[David Mazer]

The 1"/min reduction is recommended by Rocket in the supplement.  I have a JPI and it does show when cooling rate starts to be a problem and at 1"/min it is never a problem.  I use completely different procedures for non-turbo engines.  My discussion is pretty specific to what is recommended for this plane (the Rocket) by the designers.  My real question is how correct they may be.  Regardless, I have been following their advice in an abundance of caution.

[lahso]

In my C model, I use 1" per 1000ft, at a 500 FPM descent. This is based on ATC allowing a "standard" descent, with time/nautical miles to do so. Half the time, I end up immediately throttling to 20" and a 6-800 FPM. If I don't I'll end up at redline or above, and unable to slow to gear down speed when necessary.

[DaV8or]

Quote: danb35

Lycoming recommends cooling at no more than 50 deg F/min.  Just to be on the safe side, I've set the warning on my engine monitor at 30 deg F/min--and I find it's just about impossible to hit even the 30 deg. limit, much less the 50 deg.  Of course, I have a completely different engine, so your results may well differ, but I suspect you're limiting yourself much more than you need to, even assuming that shock cooling is a legitimate issue.

[Parker_Woodruff]

There's no reason to quickly pull power, except in an emergency situation that requires such actions.  However, most of what you hear about shock cooling isn't true.

[Immelman]

There are a number of techniques at your disposal. The common thing is that our airplanes pick up speed in a hurry when going downhill, so planning where to start your descent is probably the most important thing. I find a 500fpm cruise descent comfortable and quick, and I can go at a slightly reduced airspeed if necessary (pull power back and/or lean to LOP) in the event of turbulence.

To set up for this, I take a look at the GPS ETE to destination, my altitude (thousands AGL above destination), and start my descent @ 2x that figure -- e.g. 20 minutes out @ 10K AGL. This works nicely because you can quickly calculate how you're doing on the way down and adjust your rate of descent. Planning to descend *to* airport elevation rather than TPA allows you to level off a bit before the airport to slow to traffic pattern/gear speed; on a straight-in you'll probably be a bit hot.

WIth practice you'll see that the above is a starting point that you'll adjust as you figure in how the wind aloft changes with your descent, and how true airspeed will decrease along your descent.

As for power, I typically pull RPM back to 2350 (my E model as an engine/prop combo that restricts continuous operation between 2100-2350), and keep the throttle wide open if I was cruising at a high altitude. I will start to slowly retard the throttle as I descend to keep about 20" (+/-) manifold pressure. These numbers work well for my E model which has relatively low airspeeds (150mias Vno, 189mias Vne); you may have to adjust them to suit you.

Another technique I'll use, sometimes, is to lean out so that all cylinders are lean of peak at the start of the descent and fly it that way.

Yet another technique I use if I am really high and want to come down faster is to pull RPM back to 2000 or so, lean to LOP, and again slowly retard throttle to keep 20", or maybe less. This can give me a 1000fpm descent rate, not too much airspeed, the airplane is quiet, and just barely sipping fuel. I tend to avoid fast descents if I can unless necessary for terrain, etc.

I've found that the above will allow the engine to cool quite slowly (I have an engine monitor that measures and alarms if the cooling rate is excessive).

Finally, if for some reason you do realize in your descent that you're high & fast, or just have to (ATC, terrain), remember that there's nothing wrong with a 360 degree turn. That is the least expensive speed-brake you have (i.e. compared to installing speedbrakes as some Mooneys have) adds only a couple minutes to your flight, and in my opinion is preferable to pushing the airspeed up too high as you get closer to the ground where turbulence is more often a factor.

[jetdriven]

You can also  leave the mixture it ints cruise setting as well as the throttle, or lean further LOP and just leave the throttle full, and set power with fuel flow. If you are getting high or fast, lean further. Somwhere like on downwind, set MP to 15", go to ROP,  and continue as per POH.  works for us.  Full throttle from takeoff until abeam numbers.

 

 

[Hank]

It's really very simple to count thousands of feet from TPA to cruise and double it. Start down that many minutes out; request descent if necessary. Push the yoke to hit 500 fpm, and trim out the pressure. RPM stays where it was.

Yes, IAS increases going downhill--this makes up a little for the initial climb. I just watch MP and EGT, and whenever either one has moved significantly, I put it back to the original cruise values. Once I level off, then I start watching IAS and slowing down for the pattern. Vintage birds have gear speed lower than flap speed, so there's no drag bucket to slow us down.

Tuesday evening coming home, I was cruising at 8000, WOT [~21½"], 2500 RPM, ~50ROP, ~142 MPH. Started downhill:  whenever MAP hit 23", I pulled it back to 21"; whenever EGT rose near 1500, I pushed forward to 1450 or a little below; IAS topped out around 170 MPH [yellow starts at 175]. Leveled off at 3000, then 2500 before cancelling and heading home VFR in really bad haze. At 21"/2500 she slowed back down to around 140 MPH; as I maneuvered for downwind entry, I pulled back to 15-16", and entered downwind at 1600 msl with speed dropping towards 100 MPH. White arc is 125; Vg is 120 MPH. Dropped flaps, retrimmed; dropped gear, pulled throttle back a little and started down at 90 MPH, slowing to 85 MPH on final, over the trees with a loaded plane at 80 MPH, kept a little power in until I cleared the road and the drop-off, idle over the numbers, touchdown on Stripe #3. Lunch runs with no luggage are a little slower and usually idle power before the trees. If I can figure it out, I'll post a landing video on youtube--final approach to squeak/squeak is 22 MB using a Sony camera in video mode.

You turbo guys and Rocket/Missile conversions have a little more work to do, but it does pay off handsomely in speed and ability to outclimb weather.

[butchgilbert]

Hank, I use almost the same identical technique on my 1975 M20F Executive.  I try to keep the MP above 21" in the descent, V/S about 500 fpm, same pattern entry technique.  Keep the engine nice and toasty in the descent, until you have to pull it back to enter the pattern, slow down, configure and land.

[jlunseth]

First there needs to be a little better definition of "descent."  It is an entirely different thing to bring a plane down from the Flight Levels or low teens, than to bring it to 1,000 from 6,500.  If you are in the higher altitudes it is often because the winds aloft are favorable, so you may have a ground speed of over 200 kts., sometimes well over 200 kts.  My best so far is 242.  I do any long descent simply by tipping the nose over and setting the trim for my desired vertical speed, typically in the 500-700 range.  That is least likely to hurt passengers' ears.  Descent rates in the 1,000-2,000 range work for me personally, my ears clear easily, but not all passengers are that lucky, or they may not know ear clearing.   The math for a long descent is pretty simple, if you descend at 500 fpm, and you are 30 minutes out, then you will lose 15,000 feet.  In actuality, you are going to pick up a good deal of speed by tipping the nose over, so better start that descent at 33 or 34 minutes or you will wind up high over the airport.  If you are coming in too fast, and are going to be high, you can always bring the throttle back.

In this type of descent, I bring the throttle back about an inch to an inch and a half when I tip the nose over.  This is because the MP will increase about that amount simply because there is less load on the engine and the airspeed is faster, so throttling back by this amount basically means the MP will stay the same in the descent (at least initially) as it was at cruise.  Of course, as altitude changes, and in most Mooneys (those that do not have "self adjusting" turbo wastegates, or are not turbo at all), you are going to need to decrease MP as you descend, to compensate for higher air density.  The goal is to maintain a constant MP.  Cowl flaps, if you have them, should stay closed.

This procedure has the benefit of keeping the engine nice and warm during the descent.  It also has the benefit of giving you an aproximate average TAS over the length of your trip, the same as your cruise TAS.  In other words, your climb TAS and descent TAS will average out somewhere around your cruise TAS.

For shorter descents, I am not a believer in shock cooling unless you are flying in below zero temps at ground level.  In that case, temp drops can be pretty dramatic.  We do have that issue where I live, so my winter procedure is different from the rest of the year.  Other than winter, I just do what is necessary for these shorter descents.  Typically a combination of the "tip the nose over" technique, and the throttle back technique as I get closer to the airport, so I don't need to slow from a TAS in the 180-190 range (or more), which is what the "tip the nose over" technique will get you.

My plane flies at 120 IAS in the mid-24 range, i.e. 24.5 or so, so I usually throttle back to that MP about 20 out from the airport.  That gives the plane time to slow down to Vge.  Dropping the gear will then get me between 90 and 100 KIAS near the airport.

I am told by my A&P that this equation changes somewhat for the post-252 aircraft.  The Bravo's, Ovations, and Acclaims are slick enough that speedbrakes are needed, when doing the "tip the nose over" method, to keep from exceeding Vne.  I have speedbrakes in my 231, but don't need to use them often because I would really have to push things to get to Vne, even in a descent. 

[Hank]

I typically cruise at 7-11K when crossing the Appalachians, where MEAs run to near 9000'. Shock cooling is not a concern, and I happily let gravity repay some of the fuel burned to reach altitude. 500 fpm is nice, the speed will build, and I pull the throttle back to maintain cruise setting until I level off. Same for the mixture--as the air thickens, the mixture has to go forward to maintain cruise EGT. While I have been higher than 11,000 in my C, I don't cruise there often, and the climb rate is pretty abysmal.

For short feed runs at 3000 msl, I don't usually do much of anything beside push the yoke forward and retrim, then at TPA I pull the throttle back and slow down. Gear is actually 5 mph slower than flaps, so no help there . . . throttle back, trim for level, and if I'm still too fast, I have a 3-bladed speed brake out on the nose to push forward [and a note to self, don't wait so long the next time].

[fantom]

....and I'm sure we all enrichen a bit as we decent, right?

[Hank]

Quote: Hank

Same for the mixture--as the air thickens, the mixture has to go forward to maintain cruise EGT.

[fantom]

Quote: Hank

 From the end of my first paragraph above . . .

[Parker_Woodruff]

Quote: fantom

....and I'm sure we all enrichen a bit as we decent, right?

[Shadrach]

I'm a LOPer and I do the following. It is not Gami or APS's method, but my own. YMMV...

I enrichen in descent to keep the combustion event out of the exhaust (you'll see an EGT spike when this happens) as the mixture gets leaner in the thicker air. When approaching pattern altitude I'll set the EGT to the target take off target ~EGT or a little less if I'm still high. Perfect set up for a go around regardless of DA. Never had to use it thankfully.

[jetdriven]

I agree with both above.  Set it LOP in cruise, note the GPH (around 7.5-9 in a J). Note this at top of descent. Leave MP at full.   Keep the mixture at that cruise FF, which is progressively further LOP as you descend. Good, helps you get down. If getting high on your profile lean more and / or bring prop RPM back to 2000 RPM.  Usually you dont have to touch the mixture for several thousand feet.  Near the pattern switch over from LOP and lots of MP to 18" and peak EGT or a little on the rich side of peak.  MUCH simpler than moving the MP and mixture so much. 

[Hank]

When I try to go LOP, it makes the carbureter burp, and that makes the engine stumble repeatedly. Neither I nor the installed GPMS care for that. I fly near peak at 10K, a little richer belwo that, and richer yet below that.

[jetdriven]

Yeah Hank I keep forgetting you are carb'd.  In that case do you keep it leaned to edge of smooth on descent?